This invention relates generally to an arrangement and method for obtaining improved drawbar performance and added utility of agricultural wheeled tractors. Reference is made to U.S. Pat. Nos. 4,402,357 and 4,508,150 and to U.S. patent application Ser. No. 667,572 now U.S. Pat. No. 4,603,916, filed Nov. 2, 1984, the disclosure of which are incorporated herein by reference.
In the above documents the shortcomings of the pneumatic tire for a tractor's drive wheels are reviewed and methods and means for improving both productivity and for reducing soil compaction are shown. As can be concluded from these documents, much of the tire's shortcomings stem from the great variety of tasks a typical tractor is called upon to perform.
The tractor got its name because it develops traction to pull drawbar loads; notably, for pulling in fields. Not only do the widely varying field conditions call for different design criteria at the tire/soil interface, but pavement and hard ground present yet another set of circumstances. In an effort to satisfy the various demands, not only does any given size tractor come in different configurations, such as two-wheel-drive and four-wheel drive, but it also offers several drive wheel options--such as dual tires and auxiliary wheel weights. In addition, tire manufacturers are making available a great number of tire tread designs, which are available for regular bias type tires as well as for radial type tires.
Even with the proliferation of choices, there are trade-offs. An example in regard to tire tread designs is the so-called Rice & Cane, designed with high tire lugs for traction in wet rice fields. For traction, such tread design is useful in other fields as well. However, as tractors are used for pulling on roads and hard ground as well--in such use this design exhibits serious problems both in respect to traction and to tire wear; for such uses, its extra costs is rarely justified.
It is well known in the art that, (a) for best performance in fields the higher soil-values of the sub-surface layer of soil must be taken advantage of, calling for deep and aggressive tire lugs; and (b) for best performance on roads and hard grounds, the more rubber at contact-surface the better, thus calling for shallow or no tire lugs. The present invention addresses both of the above performance criteria by employing ultra-high strength steel spades, which are expeditiously engaged and retracted, in combination with tires with smooth or shallow tread.